In a mobile telecommunications network, for example, it may be necessary to locate the position of a mobile telephone transceiver or handset within a given cell of the network. A system is known whereby a small number of cell sites within the network are used to measure the amplitude of the signal emitted by the user's mobile telephone handset. The set of amplitude data is then compared with a pre-existing set of reference data, which is generated by moving a transmitter to all points in a grid of locations within the coverage area of the network. By comparing the data set obtained by measuring the amplitude of the signal of the actual mobile telephone handset with the reference data set, is an estimation of the location of the mobile telephone handset, and hence the user, can be obtained. Such a system is described in GB-A-2 352 134, GB-A-2 291 300, GB-A-2 311 697, WO-A-98/15149 and EP-A-0 133 378.
This system is particularly used to locate users who, for some medical reason, for example, have contacted the emergency services but are unable to give their precise location.
It is a disadvantage of this system that the reference set of data must have been generated in order to compare it to the signal amplitude data and hence locate the mobile telephone handset's position. Furthermore, the actual set of data may be affected by local irregularities, for example weather conditions, which are not reflected in the reference set of data.
German Offenlegungsschrift DE-A1-2849 282 discloses a system which is suitable for determining the distance between a mobile telephone and a base station and relies upon a line of sight signal. Signal strength and distance are related by a 1/r2 power function.